1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, which is applied to a variety of relatively sliding portions in machine tools and testing equipment and in which a slider is mounted slidable on a track rail with rolling elements interposed therebetween.
2. Description of the Prior Art
In conventional linear motion rolling guide units, the sealing between a track rail and a slider that slides on it is realized by end seals attached to the ends of the slider and under seals attached to the underside of the slider.
A linear motion rolling guide unit as shown in FIG. 5 has been known. FIG. 5 shows a perspective view of one example of a conventional linear motion rolling guide unit. As shown in the figure, the linear motion rolling guide unit includes a track rail 1 having raceway grooves 9 extending longitudinally on both side wall surfaces 8 thereof, and a slider 18 slidably mounted astride on the track rail 1. The slider 18 has a casing 2, which is slidable relative to the track rail 1 and has raceway grooves 7 formed at positions facing the raceway grooves 9 on the track rail 1, a number of rolling elements 4 trapped between the opposing raceway grooves 7 and 9, and end caps 5 attached to the longitudinal ends of the casing 2, the longitudinal direction being the sliding direction of the casing 2. The end cap 5 has an end seal 27 attached to the end surface thereof that provides the sealing between the track rail 1 and the slider 18. The end cap 5 is also provided with a grease nipple 26 for supplying lubricant to the sliding surfaces between the track rail 1 and the slider 18. To prevent the rolling elements 4 from coming off the casing 2, retainer bands 24 are provided to the casing 2 in such a way as to enclose these balls 4. The under seals 3 have a function of retaining the rolling elements 4 in place and also a function of sealing the sliding portions between the casing 2 and caps 5 and the longitudinal side wall surfaces 8 of the track rail 1. For this purpose, the under seals 3 are arranged at the undersides of the casing 2 and the end caps 5.
The slider 18 is mounted astride on the track rail 1 and freely slidable relative to it through a number of rolling elements 4 circulating along the raceway grooves 9 in the track rail 1. The rolling elements 4 that travel loaded along the raceway grooves 9 of the track rail 1 are led to direction changing passages formed in the end caps 5 and further to return passages 25 formed in the upper part of the casing 2 parallel to the raceway grooves 7. Thus, the rolling elements 4 run endlessly through endless circulating passages. In this way, the slider 18 is allowed to slide relative to the track rail 1 by the rolling elements 4 traveling loaded between the raceway grooves 7 on the slider 18 and the raceway grooves 9 on the track rail 1.
The under seal 3, though it has an advantage of being thin and simple in construction and easily manufactured, also has drawbacks that because the under seal 3 is thin, it is easily deformed by external forces and by positioning errors between it and the casing 2 and track rail 1, the casing and track rail having the raceway grooves 7, 9 respectively.
In an under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 118317/1991, axial ends of the under seal are formed with axially extending projections and end seals are formed at their bottom end surfaces with engagement holes for receiving the projections of the under seal, whereby the under seal is fitted into the end seals having a greater strength to make mounting and dismounting easy and to secure a sufficient strength.
In another under seal apparatus for a linear motion guide bearing disclosed in the Japanese Utility Model 121220/1991, the axial ends of the under seal are provided with two-pronged projections protruding toward the underside of the slider, the two prongs diverging in a V-shape and being elastically deformable toward each other. The slider has the axial end portions of the underside thereof formed with vertical holes, into which the two-pronged projections of the under seal are fitted, and also with through-holes that intersect the vertical holes perpendicularly and pass through the arm or wing portions of the slider. One of the two prongs fitted into the vertical hole is elastically deformed therein, urging the under seal toward the side surface of the guide rail to bring the side edge of the under seal into sliding contact with the guide rail.
In these under seal apparatuses for the linear motion guide bearings, the under seal is mounted by engaging the projections or prongs formed on the under seal into the engagement holes formed in the slider or and seals.
The conventional linear motion rolling guide units, however, uses different materials for the dust prevention member and the slider, so that they have different thermal expansions as temperature changes. When the thermal expansion of the dust prevention member becomes larger than that of the slider, the dust prevention member will be deflected creating a gap between it and the guide rail or the underside of the casing, with the result that the sealing performance deteriorates, unable to prevent ingress of dust.
To solve the above drawback, the applicant of this invention developed a linear motion rolling guide unit and applied for patent previously (Japanese Patent Laid-Open No. 164128/1993). In this linear motion rolling guide unit, the under seal has a lip portion sealingly engageable with the undersides of the casing and the end caps and another lip portion sealingly engageable with the side wall surface of the track rail. The under seal is also formed at the longitudinal ends with locking portions, which are fitted into engagement holes formed in the end seals to mount the under seal to the end seals.
In the conventional linear motion-rolling guide unit, since the longitudinal ends of the under seal are engaged in the engagement holes formed in the end caps or end seals to mount the under seal to the end seals, there must be some play for the under seal to move relative to the undersides of the casing and end caps so that the longitudinal elongation of the under seal due to thermal expansion difference can be offset by the engagement holes in the end caps or end seals. Otherwise, the under seal would be deformed as by buckling, degrading the sealing performance.
The contentional linear motion rolling guide unit, however, has the construction in which the projections of the under seal are engaged in the engagement holes in the end caps or end seals in such a way that they cannot move in the longitudinal direction. Further, since the under seal adheres to the undersides of the casing and end caps, the under seal cannot move.